The present invention relates to combine harvesters and, more particularly, to improvements in the cleaning apparatus of such machines that sifts the threshed crop materials to provide clean grain, free of chaff and other residue.
A combine harvester is provided with many systems, any of which can limit productivity, i.e., gathering, feeding, threshing, separating, cleaning, propulsion, engine power or numerous conveying mechanisms throughout the combine in reaction to the crop or field terrain conditions. Within the cleaning system, oscillating sieve assemblies in conjunction with air flow remove chaff and other residue from the threshed grain, which gravitates through the bottom sieve assembly to an oscillating clean grain pan. The clean grain pan, in turn, directs the clean grain to a discharge auger that elevates the grain to an onboard storage bin. A second oscillating pan directs materials other than grain over the edge of the bottom sieve assembly to a different discharge outlet for recirculation back through the threshing, separating and cleaning apparatus to extract the previously unthreshed grain.
It is known in the prior art to sufficiently incline the pans such that gravity pulls the material down the pans at a high enough rate of flow to not be a limiting factor. However, it is also desirable to minimize the downward pan angles in order to reduce overall combine height. Thus, these two objectives are in tension with one another. Fortunately, by continuously oscillating the pans, a lower pan angle can be used because the dynamic friction is more easily overcome by gravity than the larger static friction. Notwithstanding the assistance provided by oscillation, however, prior art machines have sometimes experienced situations in which conveyance stops altogether at lower pan angles, resulting in complete failure of the cleaning system. The problem is particularly prevalent in hill climbing as the inclined pans become more level.
The present invention provides a cleaning apparatus for combine harvesters that can improve the throughput of the machine. It involves in part the recognition that in prior art machines, part of the problem is that the feed stroke of the oscillating pans is opposite to their direction of conveyance. As the pan angle decreases in these machines, a critical point is reached at which conveyance stops altogether. For purposes of this discussion and the detailed description and claims which follow, xe2x80x9cfeed strokexe2x80x9d refers to that stroke during each cycle of oscillation in which the pan or sieve experiences an upward component of travel, while xe2x80x9cretract strokexe2x80x9d refers to the stroke in which the pan or sieve experiences a downward component of travel.
In a preferred form of the invention the cleaning apparatus includes as primary components an oscillating sieve assembly, comprising a pair of superimposed sieves, and a counter oscillating pan assembly below the sieve assembly. The pan assembly comprises a clean grain pan stacked above a lower tailings return pan. The sieve assembly is coupled to its operating mechanism in such a manner that both sieves, moving in unison on a common frame, have their feed stroke in the same direction as their direction of conveyance. This assures that residue particles too large to pass through the sieves are urged in the direction of conveyance by an effective upward xe2x80x9ctossingxe2x80x9d action as the sieves shift toward their discharge points.
The pan assembly is totally separate from the sieve assembly and is thus moveable in a distinctly separate motion in the most advantageous way, i.e., the feed stroke of the pan assembly is in the same direction as its direction of conveyance. Instead of having one of the sieves mounted on a common frame with the clean grain pan and the tailings return pan as in the prior art, the present invention contemplates having the grain pans mounted on their own frame completely separate from the sieves. Thus, the sieves can be moved in a direction that is most advantageous for the sieves, while the pans can be moved in directions that are most advantageous for them. Furthermore, the clean grain pan, and optionally the tailings pan, is provided with a corrugated top surface of generally sawtooth construction, with the corrugations being inclined generally in the direction of conveyance so as to maximize feeding efficiency.